1. Field of the Invention
The present invention relates to an image processing circuit of a semiconductor image sensor, such as a CMOS image sensor and a CCD image sensor, and more particularly to an image processing circuit of an image sensor providing improved image quality by suppressing such noise as moiré that generates for each column.
2. Description of the Related Art
A CMOS image sensor, an example of a semiconductor image sensor, comprises a pixel array where pixels having photoelectric conversion elements, are arranged in a matrix, wherein a color filter, such as RGB, is disposed on the pixel array, and each pixel outputs a photoelectric conversion signal matching the gradation value of each RGB corresponding to the color filter. In the row direction of the pixel array, row select lines for selecting each pixel and reset lines for resetting the potential of each pixel are disposed, and in the column direction of the pixel array, column lines for propagating the photoelectric conversion signal of each pixel to the column output circuit are disposed. In the column lines, a column output circuit, which has such functions as amplifying the photoelectric conversion signal and removing the reset noise thereof, is disposed respectively, and the output signal of the column output circuit is supplied to the image processing circuit via the output bus.
The image processing circuit, which is also called a color processor, performs sensor sensitivity correction, color interpolation processing, color adjustment processing, gamma conversion processing, and output format conversion processing, and outputs image signals in the desired format.
Such a CMOS image sensor is disclosed in prior art, stated in Japanese Patent Laid-Open No. 2002-218324.
In the image sensor, the column output circuit is disposed for each column, and a pixel signal, which is an output signal of the column output circuit, is supplied to the color processor via a common output bus. Each column output circuit and the circuit for supplying pixel signals from the column output circuit to the color processor are in a parallel configuration, and are designed such that characteristics do not disperse depending on the column.
However, if an image is displayed or output by the image signals generated from the image sensor, vertical moiré is generated regularly or irregularly in the output image. When images with uniform color are output, in particular, such vertical stripe patterns may stand out.